Two indigenous cases of West Nile virus detected in Ile-de-France, a first

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For the first time, indigenous cases of West Nile fever, also known as West Nile fever, transmitted by mosquitoes, have been observed in the Île-de-France region, health authorities announced on Wednesday, August 13. At the same time, outbreaks of chikungunya are increasing in France at a particularly high level.

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"Two indigenous cases of West Nile virus infection have been detected in people living in Seine-Saint-Denis," the Île-de-France regional health agency summarized in a press release . "These are the first identifications of local vector-borne transmission of West Nile virus in Île-de-France."

This virus is transmitted through mosquito bites. However, unlike chikungunya or dengue fever, it is not the tiger mosquito that is responsible, but the Culex mosquito, which is much more widespread in France.

Another difference from these two other diseases is that West Nile fever is not transmitted from human to human by mosquitoes, but from an infected bird, which the insect bites.

The infection is usually asymptomatic, but in about one-fifth of cases it results in a flu-like illness. In less than 1% of cases, serious complications can occur, sometimes leading to death.

Indigenous cases, resulting from local contamination, have already been reported in mainland France in previous years – around forty in 2024 – but never so far north.

This summer, apart from the two cases in the Paris region, five other indigenous cases were recorded in the south, in Provence-Alpes-Côte-d'Azur, the national agency Santé publique France specified in another report, published this Wednesday.

Public Health France also continues to monitor the development of indigenous cases of chikungunya in France on a weekly basis. These cases are at a particularly high level this summer, following an epidemic in Réunion Island that facilitated the importation of the virus. According to Public Health France, "23 episodes of chikungunya totaling 115 cases (with) 1 to 23 cases per episode" have now been recorded in France, adding that six of these episodes have been closed. The previous week, the total stood at 16 outbreaks for 63 cases, already a record level.

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